The present invention relates to a plant operation method and a plant operation control system having a plurality of different type equipments. More particularly, the invention relates to such a method and system suitable for district heating and cooling systems, cogeneration systems, fuel cell systems, and other systems.
For example, the following conventional techniques are known as an optimal operation method for equipments.
(1) JP-A-61-97703 (hereinafter called a conventional technique 1). PA1 (2) "Optimization of Cogeneration", by Kouich ITOH and Ryouhei YOKOYAMA, issued by Sangyo Tosho K.K., pp. 45-63 (hereinafter called a conventional technique 2). PA1 (3) JP-A-4-93558, "Operation Control System for Refrigerators (hereinafter called a conventional technique 3).
The conventional technique (2) is concerned with an operation method for a cogeneration plant constituted by equipments such as generators, boilers, and refrigerators. With this method, an operation efficiency of each equipment is formulated by linear programming, and a schedule of a start/stop state and a schedule of output level of each thermal source equipment are determined by linear programming while minimizing an operation cost which is used as the objective function.
The conventional technique (1) is concerned about an operational planning method for a plurality of thermal source equipments. With this method, combinations of equipments are selected which can be realized from the viewpoint of equipment connections. The operation period is divided into a predetermined number of small periods in accordance with the operation conditions such as equipment inspection states. The sum of operation cost and start/stop cost of the combination of equipments at each divided small period is calculated, and a predetermined number of combinations starting from the combination which has the minimum sum, are selected as the solutions of shortest path problems.
The conventional technique (1) is cost effective because the optimum solution can be obtained mathematically. With the second conventional technique (2), practical combinations are predetermined based upon various conditions. Therefore, the number of combinations is small, thereby reducing a calculation amount (time). However, both the conventional techniques (1) and (2) aim at minimizing the operation cost, and do not consider the life of equipment (reliability), an irregular change in equipment performance characteristics at the start/stop, and the like.
A conventional technique (3) is also known in which a start/stop schedule of each equipment is determined while considering the life time of the equipment.
According to the conventional technique (3), the occurrence frequency of starts and stops of a compressor of a refrigerator is measured. Each time when the occurrence frequency of starts and stops exceeds a predetermined occurrence frequency, the re-start inhibition time period of the compressor and the stop inhibition time period after a start are made longer than initial values.
The equipment reliability is improved by reducing the start/stop occurrence frequency. However, the conventional technique (3) regulates only the start/stop occurrence frequency of a single equipment, and does not determine an operation by considering equipment performance characteristics, continuous running state, influences to other equipments, and the like.
As an optimal operation method by which an operation method of thermal equipments are determined from given future demands, there is known a method of formulating performances such as efficiencies of equipments and economically determining an operation method through mathematical programming by using as the objective function an operation cost such as a consumed fuel (electricity) charge.
In order to obtain a practical operation method, it is necessary to consider also the life of equipment (reliability), irregular equipment performance characteristics at the start and stop, and the like.
Generally, it is necessary to reduce the number of start/stop times of a thermal source equipment such as a boiler, generator, and refrigerator as many as possible because the equipment has a large heat capacity and because the lifetime of the equipment is adversely affected by thermal stress and temperature change at the start/stop which may result in deterioration of electric insulating materials.
The conventional techniques determine start/stop schedules at each operating time period which minimizes the energy consumption cost of thermal equipments. Therefore, the combination of equipments changes with demands which change with time, resulting in an intermittent operation having a number of start/stop states. As a method of reducing the number of start/stop states by optimization through linear programming, it is known that a cost required for start/stop is determined and added to the objective function. With this method, although the number of start/stop states can be reduced, combinations of equipments are determined without considering past and future operation conditions, being unable to obtain a practical solution. Although dynamic programming determines an optimum solution by considering past and future operation conditions, dynamic programming requires a tremendous calculation time as compared with the linear programming. Dynamic programming is therefore difficult to-be used practically.
With conventional mathematical programming, the number of parameters to be processed becomes great if important equipment operation conditions such as equipment life times and equipment output response characteristics, are to be taken into consideration, or it becomes necessary to use dynamic programming which requires a very long calculation time. In the case of a large scale and complicated equipment configuration, particularly in the case of a district heating and cooling system, a calculation time increases greatly so that dynamic programming is not practical,
As a result, conventional optimization through mathematical programming is difficult to consider necessary operation conditions such as equipment life times and equipment output response characteristics. Accordingly, an actual equipment operation has been conventionally relied upon intuition and experience of a skilled operator in many cases. Optimization by the decision of an operator is however unreliable, and the decision differs from one operator to another. Furthermore, a need of an automatic operation has been strongly desired because the number of available operators tends to be insufficient.